The present invention relates to the separation of gases into components of differing boiling points. The invention relates more specifically to a method and an apparatus especially suited for separating propane, methane, ethane or carbon dioxide from natural gas.
The applicant's prior U.S. Pat. No. 4,770,683, issued Sep. 13, 1988 describes a process and an apparatus for distillation of two materials of differing boiling points. A process for distillation of two materials of differing boiling points particularly propane, ethane or carbon dioxide from natural gas is described in which the conventional distillation tower is divided into a first tower at higher pressure than a conventional tower and a second tower at lower pressure. Liquid drawn from the first is expanded to the lower pressure through two or more stages with cool extracted at each stage and used to cool gas withdrawn from the top of the first tower to keep the top tray at a required temperature. Gas withdrawn from the second tower is compressed and cooled for return to the first tower as a reflux. The use of the cool from the expanded liquid and the use of the two towers provides an improved thermo-dynamic efficiency and avoids the use of costly turbo-expanders.